>Hello group,
>
>
>I am trying to repair an old Henry 2K. It is the original 2k console unit
>with a pair of 3-400Zs and the power supply which uses the two tube
>rectifiers. The two rectifiers were replaced with the Intl Rectifier 1nxxx
>type units.
>
>
>When the unit is powered up the primary fuses blow once the HV switch is
>enabled.
>The filament power appears to be ok. I have removed the tubes and
>ruled out any kind of tube short. It appears that if the amp is stone cold,
>there is a slight delay before the buzz and blown fuse event takes place
>when
>the HV switch is thrown. Once it is warm, it trips right away. I did some
>simple troubleshooting, and there appears to be no short of any kind on the
>HV line (with the Ip meter disconnected, otherwise it gets in the way of
>checking to ground). The only thing I could not confirm was the two solid
>state rectifiers. When measuring from the base to the anode, I get an open
>reading in both directions. Is there a way to test these that I am not aware
>of?
To test a HV rectifier stack in the fwd direction, one needs around 1v
per kV of piv rating, limited to c. 0.5A with a series resistor. The
V-drop across the stack should be c. 0.7v per kV @ 0.5A. To test piv,
apply enough reverse potential with a high-pot tester to see 2uA of
reverse I. The applied potential is the piv. If the reverse current
fluctuates randomly, the diode stack is not good.
> ratingWhat kind of reading should I expect when checking them? Could they
be
>the culprit?
>
>Also, while the choke appears good, could it be failing once under load
>(powered up)?
This is pretty common for older resonant chokes that are not potted. I
would dry the suspected choke out in the oven for a few days at 200ºF,
and then pot it with laminating resin. Instructions for home-potting are
on my Web site. I would also install two, 10?, 10w, glass-coated
resistors in series with the +HV between the filter C and the HV-RFC.
This is called a "glitch resistor". A better parasitic suppressor design
might be a good idea too since the 2K reportedly has an intermittent
parasite just below 100MHz. However, better suppressors cost c. 2% of
the output P at 29MHz.
good luck, Eric
- R. L. Measures, a.k.a. Rich..., 805.386.3734,AG6K,
www.vcnet.com/measures.
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